It is known that the operations to lay, stretch and/or replace electric cables, optical fibres, ropes or similar are usually performed using machines called winches, brakes or winch-brakes, comprising two or more combined pairs of driven capstans, made to rotate by respective hydraulic motors, so as to simultaneously lay one or more cables at once.
In a laying plant, the drawing machine (winch) determines the unwinding speed of the cables from the respective capstans, while the brake machine determines the tension thereof.
In order to lay the cables, drawing pilot ropes, or the electric cables which are already on the lines and have to be replaced, are normally used.
Due to operating necessities linked to the laying procedure, and to ensure an accurate and precise control during stretching, the cables collected simultaneously from several combined capstans of the drawing machine must have the front ends which maintain their starting alignment for the whole operation. In practice, however, it is difficult to maintain this alignment for various reasons: in fact, the cables can wind onto their respective capstans differently from each other; the capstans of the same winch can have respective different rotation speeds caused by the different hydraulic losses of the circuits which feed the hydraulic motors, or due to different mechanical friction relating to the line which is being stretched (pulleys, different heights, etc.).
In the state of the art, to solve this problem, the capstans are constrained mechanically to each other by means of at least a clamping pin and drawn by means of a common drawing rope.
In this way, the cables are obliged to constantly maintain the same speed of rotation, hence theoretically ensuring that the cables are aligned for the whole of the laying step.
Although this solution partly solves the problem of alignment, it does however create other problems; for example, if it is necessary to stop one of the capstans, the operator is obliged to interrupt the drive to all the other capstans, to unconstrain the capstans, to solve the problem which has caused the stoppage, to realign the cables, to mechanically constrain the capstans to each other again and to start laying again.
All these operations need a lot of time to carry out, and are necessary even for minimal interventions which take only a few minutes maintenance; this causes a considerable waste of time and hence of productivity in the laying operation.
In any case, the use of a common drawing rope to draw an ever increasing number of cables entails an increase in costs due mainly to the considerable mechanical drawing capacities required from the rope which, according to the number and type of cable, is bigger and bigger.
In this context it must be considered that the current increase in the demand for electric energy and/or data transmission connections entails a parallel increase in the carrying capacity of the individual lines, with a consequent increase in both the size and number of the conductor cables themselves.
We therefore have a progressive increase in the laying costs and times, due not only to the oversizing of the drawing cables but also to the necessary increase in the sizes and operating capacities of known machines used for drawing and laying. In fact, for such operations combined machines are normally used, which have to support a large number of capstans.
In order to partly obviate this disadvantage, it is known to divide the overall number of bundles of cables into multiples, using a large number of known machines and equipment, each with a limited number of capstans.
But this known solution also entails operating and applicative limits, due especially to the complexity of the known machines used which have to guarantee high operating performance, and the need to guarantee synchronized laying of the cables.
Documents U.S. Pat. No. 5,048,797 and EP-A-972.669 describe devices suitable to lay a single cable, with the cable remaining still and the laying machine moving. These documents refer to systems to synchronize the speed of the laying machine and the tension of the cable, but do not attempt to solve the problem of synchronizing the speeds of two or more cables laid simultaneously by laying machines which stay stationary with respect to the ground.
One purpose of the invention is to achieve a synchronization device for plants and machines for laying and stretching a number of cables, even a large number of cables, such as for example electric conductors, optical fibres, ropes or similar, which will allow, in a simple and effective manner, to keep the leading ends of said cables constantly aligned with each other as they simultaneously unwind from several capstans of two or more different machines, during the laying steps.
Another purpose of the present invention is to achieve a synchronization device which will allow to perform the steps of simultaneous laying of a large number of cables, substantially reducing the costs and times of intervention, yet in any case guaranteeing a good alignment of the cables.
Another purpose is to achieve a device which will allow to operate individually on each of said cables, and on the relative capstans, without having to interrupt the functioning of the entire machine and hence of the other capstans.
Another purpose is to achieve a device which will allow to command several machines to lay or collect cables with only one operator, thus substantially reducing labour costs.
The Applicant has designed and embodied the present invention to overcome said shortcoming of the state of the art and to obtain further advantages.